A water polo ball is a ball used in water polo and canoe polo, usually characterized by a bright yellow colour and ease of gripability, so as to allow it to be held with one hand despite its large size. Ball weight is 400-450 grams (14-16 ounces) and inflated to approximately 90 kPa (13 PSI) of pressure. Water polo balls come in two main sizes: a size 5 (0.7 meters or 28 inches in circumference), intended for use by men, and a size 4 (0.65 meters or 26.5 inches in circumference), intended for women. Smaller balls are sometimes used by juniors for "mini-polo," though these miniature do not typically come in standard sizes and are often coloured green.
In the first half of 2005, FINA allowed a change to the standard water polo ball used in official games. This change permitted a coloured middle stripe (blue, green, red, black, or yellow) with the normal yellow stripes flanking the coloured.
In May 2006, the NCAA and National Federation of State High School Associations Rules Committees announced a rule change allowing the colored balls to be used in all NCAA and NFHS sanctioned games. The current rule states that the water polo ball must be “yellow with black lines,” but new wording will allow for colored panels. Mikasa Sports, manufacturer of the new colored ball, claims that the new ball benefits teams by making it easier for them to keep track of their balls, differentiating the women’s balls from the men’s and teaching proper rotation on the ball.
Unique designs and color combinations have been used to commemorate special competitions.